1. Field of the Invention
The present invention is directed to a bearing assembly adapted for facilitating linear motion on a shaft or the like. More particularly, the present invention is directed to a bearing assembly having high weight and force bearing capacity and adapted for linearly moving an object on a shaft.
2. Brief Description of the Prior Art
Bearings are well known in the prior art. As is well recognized, bearings which facilitate linear motion of an object or machine part on an elongated member, such as a shaft or rail, must meet different requirements than bearings adapted for facilitating rotary motion. Nevertheless, such bearings (hereinafter referred to as linear bearings) are practically ubiquitous in machine tools and many other mechanical applications. Often, linear bearings must be able to withstand very high weight and force loads, and must be able to function with high precision of movement and very low friction.
One type of linear bearing of the prior art operates on the simple principle of sliding friction. In other words, a bearing surface simply slides on a suitably contoured shaft or rail. In this type of bearing, friction forces are high, and under static conditions lubricant is readily forced out from between the overlapping sliding surfaces. Therefore, this type of simple bearing binds readily, is subject to undue wear, and requires unduly high input of power to operate.
Wheel and track arrangements are often used in lieu of linear bearings. These, however, are bulky, expensive and often still fail to provide the required degree of precision.
An alternative linear bearing of the prior art includes a bushing which has a plurality of balls adapted for rolling motion between the bushing and a shaft when the bushing is moved on the shaft. Channels or guides are provided in the interior of the bushing to circulate the balls so that a predetermined number of the balls are always available for rolling between the bushing sleeve and the shaft. Such ball bushings are manufactured by Thomson Industries of Manhasset, N.Y., and are described in a brochure of said company.
A disadvantage of ball bushings is that only point contact occurs between the weight supporting or force bearing balls and the shaft, (or the balls and the bushing). Therefore, in order to provide high load bearing capacity, relatively large balls are required. This, in turn, means that no more than 5 or 6 ball return channels may be incorporated into a single ball bushing. Consequently, relatively high contact stresses occur in the ball bushings, and the ball bushing shaft assembly is relatively bulky for any given load application. Furthermore, it is subjected to relatively high degree of wear.
Still another alternative linear bearing of the prior art is known under the tradename of "ROUNDWAY bearing" of the Thomson Industries Company of Manhasset, N.Y. This bearing, also described in a brochure of said company, utilizes a plurality of rollers connected to one another in a flexible endless chain. The rollers roll between a cylindrical shaft and a likewise cylindrical bearing race. Although this bearing is capable of supporting high loads, one of its disadvantages is that it does not resist side loads. Furthermore, this bearing too, is relatively bulky for any given load application.
For still further background to the present invention, and particularly for bearings which are capable of both linear and rotary motion on a shaft, reference is made to the following U.S. Pat. Nos.: 4,025,128; 3,446,540; 3,751,121; 3,582,160; 3,037,821; and 3,692,371.
In light of the foregoing, the need in the prior art is apparent for a linear bearing which provides high load supporting capacity, high wear resistance, and is very compact relative to the loads it is capable of supporting. The present invention provides such a linear bearing.